1. Field of the Invention
The present invention relates to a conductive thin film pattern formed on a substrate and a method of forming the same, a method of manufacturing a thin film magnetic head including the conductive thin film pattern, a method of manufacturing a thin film inductor, and a method of manufacturing a micro device.
2. Description of the Related Art
Hitherto, as communication path means for passing current in an electronic/magnetic device formed by using a thin film process, a conductive thin film pattern is often used. For example, a metal thin film coil is used in a thin film magnetic head or a thin film inductor, and a metal wiring pattern is used in a semiconductor device.
As a method of forming a conductive thin film pattern of this kind on a substrate, a so-called frame plating method is known. According to the method, a resist frame having a desired opening pattern shape made by a photoresist or the like is formed on an underfilm formed on a substrate. After that, electroplating is performed by using the underfilm in an opening in the resist frame as an electrode film, thereby growing a plating film on the underfilm to form a conductive thin film pattern. This method is disclosed in, for example, Japanese Patent Publication No. Sho 56-36706.
In recent years, to reduce the size of such a device, reduction in the size of the conductive thin film pattern is being demanded. In this case, to reduce the size in plan view of the conductive thin film pattern without deteriorating the performance of the device, it is necessary to assure a sufficiently large section area orthogonal to the current direction of the conductive thin film pattern. As a result, a higher aspect ratio is requested. The aspect ratio denotes the ratio of height to width in a rectangular cross section.
To obtain a higher aspect ratio, the thickness of the frame resist has to be increased. From a viewpoint of a forming process, the thickness of a resist layer is limited and, as a result, a conductive thin film pattern having a sufficient height is not obtained for the following reason. If a resist layer is formed very thick, in a photolithography process, at the time of development of dissolving and removing the portion inside the frame, a problem occurs such that the resist frame is partly destroyed, and a high-precision pattern cannot be formed.
To deal with the problem, a method of obtaining a conductive thin film pattern having a high aspect ratio by repeating a frame plating process a plurality of times to stack a plurality of conductive thin film patterns (hereinbelow, called repetitive frame plating method) has been proposed. According to the method, even if a pattern formed by the frame plating process of once is thin, a cross section shape having a large height is obtained as a whole stack body obtained by repeating the process a plurality of times. As a result, a high aspect ratio can be obtained.
A method of forming a resist frame in the frame plating method includes a method of using a liquid photoresist as a photoresist layer (hereinbelow, called a liquid resist method) and a method of using a dry film photoresist as a photoresist layer (hereinbelow, called a dry resist method). The liquid resist method is a method of forming a resist frame pattern by applying a liquid photoresist material, curing the material, performing selective exposure with an exposure mask, and performing development of dissolving and removing an unnecessary resist portion. The dry resist method is a method of forming a resist frame pattern by adhering a film resist in a sheet shape onto the underfilm and performing exposure and development similar to the above. The method is disclosed in, for example, Japanese Unexamined Patent Publication No. Hei 8-330736.
In the case of applying the liquid resist method to the repetitive frame plating method, high-resolution patterning is possible, however, the following problem occurs. When a liquid photoresist layer as a resist frame of a second layer is formed on a resist frame as a first layer, inter-mixing occurs between the first and second layers (a phenomenon that the resist frame as the first layer is re-dissolved and is mixed with the resist layer as the second layer) and the shape of the resist pattern is lost. As a result, it is difficult to form a resist frame having high dimensional precision.
On the other hand, according to the dry resist method, the possibility of occurrence of inter-mixing at the time of forming the frame resist as the second layer is low. However, it is difficult to carry out patterning with high resolution. Consequently, the pattern pitch of the resist frame obtained is limited and it is difficult to realize the pattern pitch of about 100 μm or less.